Synchronizing problems with postgres database

I am having troubles with a postgres database in the sense that sometimes or even most of the times not all of information in a field is written into the database. E.g. writing an author name like “Miller”, sometimes only the last character is missing, so that I only have “Mille”, or sometimes more letters are missing, down to having only one letter “M” in this case. One can see this, independent which field is written to. The problem exists with 5.0, as well with 5.1.
Has this behaviour to do with JabRef or with the database, or with some timing issues?
Our IT gave me the following info: The server is “sles 12 SP5” and on it we have “postgres 10” running.

Any help appreciated. If it is a bug in JabRef, I can raise this question on GitHub as well.